No abstract

Efflux of chemotherapy drugs by P‐glycoprotein (P‐gp) at the plasma membrane is thought to be a major cause of cancer multidrug resistance. In this report, we show by flow cytometry that P‐gp also concentrates large amounts of 2 different drugs, Hoechst 33342 and daunorubicin, within a cytoplasmic compartment of multidrug resistant CHRC5 cells. A quantitative assay of Hoechst 33342 revealed that cytoplasmic sequestration by P‐gp in CHRC5 cells accounted for about half of the amount of Hoechst 33342 accumulated by the drug‐sensitive parental Aux B1 cells. Daunorubicin sequestered in the cytoplasm of CHRC5 cells could be released by inhibiting P‐gp function with cyclosporin A, resulting in cell death. A likely site of drug sequestration is P‐gp‐containing cytoplasmic vesicles, in which the P‐gp is oriented so that drugs are transported and concentrated in the interior of the vesicles. P‐gp was detected in the membranes of cytoplasmic vesicles of CHRC5 cells by confocal immunofluorescence microscopy and immunoelectron microscopy with anti‐P‐gp monoclonal antibodies (MAbs). Vesicular localization of daunorubicin was observed by epifluorescence microscopy. The origin and nature of the P‐gp‐containing vesicles are unknown, but they do not correspond to endocytic vesicles. Our results directly demonstrate that chemosensitizer‐induced release of drugs sequestered in cytoplasmic vesicles by P‐gp can be used to overcome multidrug resistance. Int. J. Cancer 76:857–864, 1998.© 1998 Wiley‐Liss, Inc.

Ca 2+ communication in glioma networksComplex multicellular patterns of Ca 2+ activity were observed in gliomas originating from xenografted patient-derived human glioblastoma cells in brains of awake mice using in vivo multiphoton laser-scanning microscopy 2,3